It is Hyrums law. The observable feature of the board was that it could bear load despite that not being the intention, and the house started using this observable feature.
Not sure if this is a joke or if you're actually that pedantic to think they purposefully left off the apostrophe because they think it's called "Hyrums law" not "Hyrum's law".
They were agreeing with the top-level comment, not correcting their spelling.